I. Field of the Invention
The present invention is directed generally to mechanical improvements in vascular catheters that has wide application. The invention applies to catheters of a type usable by cardiologists for peripheral or coronary catheterization or balloon angioplasty, embraces catheters used by electrophysiologists for performing electrical mapping of the heart or electrical tissue ablation and also involves devices used by radiologists in cerebral or any arteriography/venography procedures or cavitary visualizations or intervention. In particular, the invention endows such catheters with sharp-angle, multi-directional deflection capabilities which enables them to access and treat hard-to-reach areas such as branching vessels, or the like. The invention, in some cases, may eliminate the need for a guidewire and the time required to perform procedures such as electrical mapping to identify the source of cardiac arrhythmia may be greatly shortened and more successfully accomplished owing to the improved maneuverability of the catheter.
II. Discussion of the Related Art
Electrical mapping to discover the source of cardiac arrhythmias and subsequent electrical tissue ablation to eliminate such sources represents one important application for the improved catheters of the present invention. In addition, the heart chambers, valves and associated vessels represent a true challenge with respect to the intricacy of maneuvering therethrough and reaching remote areas and surfaces for mapping and ablation.
Normal cardiac pacing, in a healthy heart, is controlled by a special structure known as the sinoatrial node (SA node). This is the natural pacemaker of the heart and is a specialized tissue located within the muscle walls of the right atrium. The SA node provides impulses which dominate the inherent or natural rhythmic contractions of the heart atria and the ventricles. This dominance or control involves the transmission of ionic impulses through cardiac conduction pathways in the atria and the ventricles which cause the heart to contract and relax in an orderly sequence at a rate dictated by the SA node. This sequence ensures that blood flow to the systemic circulation or the pulmonary system will be maximized with each ventricular contraction. The SA node has its own inherent rate which can be modified by signals from the nervous system. In response to excitement, physical activity, etc., the sympathetic and parasympathetic nervous systems react to modify the rate.
A depolarization impulse begins with the SA node and spreads as an electrical wave from its location in the right atrium across to the left atrium and down toward the transition zone between the atrium and the ventricles where another node, known as the atrioventricular (A-V) node or junction, is located. This impulse conducts through the A-V node in a slower fashion and continues to a common pathway known as the Bundle of His between the right and left ventricles, then into multiple paths called right and left bundle branches, each bundle branch supplying one ventricle. These bundle branches then divide into an extensive network of finer paths of conducting tissue which spread from the inner to the outer surfaces of the heart and which are referred to as the Purkinje fibers. These fibers feed the depolarization impulse into all portions of the ventricular myocardium.
As long as this system is intact, impulses are transmitted normally and cardiac rhythm is maintained. The natural impulse or current flow in the cardiac conduction system, however, may be interrupted or altered by congenital defect, disease or injury which can cause the formation of scar tissue. When a sufficiently severe injury or a congenital defect is present in the cardiac conductive pathways or in the ventricular myocardium, the electrical impulses are not transmitted normally and rhythmic disturbances known as cardiac arrhythmias can occur. With respect to such disturbances, the term bradycardia is used to describe an abnormal slowing of the cardiac contractions and the term tachycardia is used to describe abnormally rapid heart action. While either of these conditions can endanger the life of the patient, tachycardia is more serious, particularly in patients having underlying heart disease.
Ventricular tachycardia and other ventricular arrhythmias have been treated with a number of drugs such as lidocaine, quinidine and procainamide. In cases of excessive sympathetic nervous activity or adrenal secretion, Beta blocking drugs have been used. In cases where drug therapy has been ineffective in preventing tachyarrhythmias, certain surgical procedures have been used to ablate the arrhythmogenic tissue either from the atrium or the ventricles. This procedure involves major surgery in which an incision through the pericardium and heart muscle is made locate the arrhythmogenic tissue, which is then frozen or surgically removed to be replaced by scar tissue.
Because open-heart surgery is a high risk procedure which requires a prolonged period of hospitalization and recuperation, a less traumatic solution is needed. In response, catheters of various types have been devised and used for diagnosing and treating a number of cardiac abnormalities to avoid the trauma of open-heart surgery. For example, as a method for resolving atherosclerotic plaque build up, stenotic lesions are now routinely opened by the use of balloon angioplasty. In this procedure, a balloon carrying catheter is navigated through the patient's vascular system to the location of the stenosis. The balloon is inflated by fluid injected through a lumen of the catheter to apply pressure to the walls of the clogged vessel, thereby opening it. Angioplasty catheterization may require sophisticated intricate vascular navigation in which acute angle catheters definitely would be advantageous.
Catheter devices have also been used to locate and ablate cardiac conduction pathways. One such device is shown in U.S. Pat. No. 4,785,815, in which a catheter tube carries at its distal end at least one electrode for sensing membrane potentials within the heart, together with a heating device used to thermally ablate at least a portion of the pathway located by the sensing device. Another thermal ablation catheter for microtransection or macrotransection of conduction pathways within the heart, which uses a resistive heating element at its distal end for highly localized treatment, is illustrated and described in U.S. Pat. No. 4,869,248. These devices are generally effective once the ablating element is properly positioned at the localized area of interest. A catheter device tip of the class described has also been developed which employs a single handle operated deflection wire control system. Such a device is disclosed in U.S. Pat. No. 4,960,134. U.S. Pat. No. 4,911,148 discloses a device in which a series of aligned spaced cutouts are provided in distal section the multi-lumen plastic tube of an optical endoscopic device together with a tensioning draw wire to facilitate unidirectional deflection of the distal tip portion of the endoscopic device. This system, however, is also limited to unidirectional deflection.
The application of electrophysiological catheter ablation procedures, for example, often is hampered by the inability of the operator to maneuver the catheter tip to the precise location of the arrhythmogenic tissue. This is primarily a result of the limited maneuverability of the catheter tube itself. The catheter tube must have sufficient strength and stiffness to be guided through the vascular system to the vicinity of the tissue of interest. This construction does not allow the degree of flexibility at the tip of the catheter needed to perform intricate multi-directional manipulations in the highly localized areas involved. Available catheters, even catheters with single deflection wire control, are characterized by inadequate control of fine movements and have tips that can be deflected only in planes parallel to the main catheter tube. They lack the ability for controlled lateral movement in other directions within the atria or the ventricles.
Most present cardiac tissue ablation procedures involve the use of radio frequency (RF) electrical current transmitted to the tissue via a catheter which is positioned as closely as possible to the arrhythmogenic site within the atria or ventricles. Radio frequency electrical current heats the tissue surrounding the catheter, creating a discrete dense lesion. In order for the patient to be cured of the arrhythmia, the lesion must be created in the area from which the arrhythmia originates. Improvement in the maneuverability of such devices could optimize precise positioning of the catheter prior to ablation.
Additional applications for highly maneuverable, multi-directional deflectable devices abound. They include peripheral or coronary catheterization or balloon angioplasty and anglographical applications.